[Hammarlund] IF Crystal Filter Question (new link)

[K3PID]

I guess the link that I put in the origianl message didn't work for
everyone. Try this one !you will need to copy and paste it to your browser
of course since this is plain text only!

http://pg.photos.yahoo.com/ph/rnharsh@sbcglobal.net/detail?.dir=2722re2&.dnm=1777re2.jpg


----- Original Message ----- 
From: "K3PID" <k3pid at sbcglobal.net>
To: <hammarlund at mailman.qth.net>
Sent: Tuesday, October 10, 2006 8:01 PM
Subject: [Hammarlund] IF Crystal Filter Question


> In reference to the IF circuit for my HQ-145. This unit uses a 455 KHz
> crystal filter in the IF chain. It is a more or less classic design with a
> phasing capacitor to balance out the capacitance of the xtal ( or create a
> notch in the passband ) and it has the added feature of a selectivity
switch
> that adds resistance to the circuit to decrease the Q and thus increase
the
> passband width.
>
>
> Look at the scope traces here:
> >
> Problem:
> 1. Changing the circuit Q by switching in resistance should have the
effect
> of increasing the passband but it appears to just shift the passband with
no
> significant change in the width.
> 2. Switching OFF the xtal filter looks like it shunts the crystal which
> should just result in the widest possible passband BUT what I am obseving
is
> a very wide stop band! Yes the curve is inverted with low response accross
> the IF passband. None of the IF transformer adjustments have any effect on
> the shape or height of the curve in the OFF position.
>
> What am I missing?
>
> K3PID
> Ron H.
>
> _______________________________________________
> List Administrator: Duane Fischer W8DBF
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